Cell cycle progression via activation of cyclin dependent kinases (Cdks) is one of the hallmarks of cancer. The action G1 Cdks, Cdk4 and Cdk6, represent an essential step from quiescent to transformed phenotype. Factors that inhibit Cdk4/6 activation have tumor suppressor qualities, and these are often inhibited in human cancers. By contrast, Cdk4/6 activators, such as cyclin D are upregulated and are associated with poor prognosis. The balance between Cdk inhibitors (such as p16INK4 family) and activators (cyclin D), while important, do not represent the sole regulators of kinase activity. The interest in molecular chaperones and their roles in cellular quality control is centered on the therapeutic potential of Hsp90 inhibitors, such as 17- AAG, that promote rapid degradation of several kinases including Cdk4. In addition, Cdc37 expression is strongly correlated with cell proliferation and is extremely low in quiescent cells and healthy adult tissues. In this pilot project, we will address the role of Cdc37 expression as an early biomarker of liver cell proliferation and in addition test the role of geldanamycin as a therapeutic agent toward HCC. Specific aim 1. Characterize the role of Cdc37 as an early biomarker of HCC. We will measure Cdc37 protein levels in sections of human liver from biopsy samples. We will determine its distribution among different cell types in healthy liver and its levels in neoplastic nodules and advanced HCC. These studies will use standard histopathological staining procedures using antisera specific to Cdc37. Specific aim 2. Determine the therapeutic potential of Hsp90 inhibitors toward HCC. We will first determine the sensitivity of primary human hepatocytes toward 17-AAG in comparison to HCC cell lines and immortalized liver cells. This will involve analysis of protein kinase stability and cell viability after drug treatment.